The CATSAT Attitude Control System

CATSAT is a small 3-axis stabilised satellite in the STEDI program, to be launched in 1999. This paper describes the development of the attitude control system, with emphasis on the control laws. The 2 primary modes are the safe-hold and science modes. The safe-hold mode uses a momentum wheel, magnetometers and torque coils, with the "B-dot" algorithm. The science mode also uses momentum bias and torque coils, with Sun sensors and horizon sensors, to maintain 3-axis control. The use of reaction wheel control is also being studied. The expected performance is demonstrated by simulations.